Strange noise near transmission while idling in park (automatic transmission)

Hey y'all.
I parked my truck yesterday after getting home from work and I was listening to the engine, Idk if I'm the only one that does this, but pretty frequently after getting home I'll just let the truck idle and I'll go around the truck and do a visual and audio inspection. (It's not that the truck has issues, it runs like a champ, but I do a fair amount of off roading so I try to pay close attention to any unfamiliar noises that the truck might make) Anyway, I heard a very faint but unfamiliar noise near the engine, or so I thought. I crawled beneath the truck and it sounded like a faint rattling or milling noise was coming from the front of the transmission. Is this normal and I just haven't noticed it before? The truck only has 68k miles on it and it shifts smooth as butter, but I'm just curious if this is anything to look into further. Thanks.

 

How good are you about regular maintenance like changing the trans fluid?

If you've done your part to keep things OK, and not abused the hell out of the truck, I wouldn't worry unless the noise got progressively worse.

The problem with these mystery noises is there is really no way to know unless you tear it all down to find out. I'm sure someone will hop in this thread and be like 'oh uh thats just your torque converter spinning' or even worse something like 'your input shaft bearing is shot and it's gonna cost you $3k to fix'.

 

Thanks. I've only owned it a year now. Time to change the transmission fluid maybe?

 

If you don't know the maintenance history, then I would suggest you start with a simple drain/fill of the trans fluid. Don't go and do a cooler line exchange right away, but change 3 quarts or so with a drain or fill, and then drive a month, and then do it again. An 09 is 8 years old at this point, and if the trans fluid has never been touched then I would advise you go at it slow.

 

If you go wheeling you probably have a rock/clump of dirt stuck in the heat shield that covers the cat. I had the same problem. Just unclamp the heat shield, clean it out/ remove debris then clamp it back on. It's about a 10 minute job.

 

Could be the flex plate.

https://youtu.be/A3mUQG1oGfo

Does it sound like this?

 

Negative, thank God lol

 

10-4. What's the logic behind partially draining and topping off vs total flush?

 

I'll look into that. I already half assed checked the heat shields (poking them to see if they we're loose or flexing easily lol but they seemed pretty clean and solid). I'll check it out more thoroughly next time though. Thanks.

 

If you tap the exhaust with a rubber mallet near that area you can hear if it rattles! I just started by the muffler and tapped forward till I found the issue. Good luck!

 

Automatic transmissions still have clutches/friction plates inside them. As the transmission ages, that friction material breaks off of the plates and finds its way into the fluid.

In the example of a transmission that has never been maintained, the worn out fluid is lacking the chemical additives that normally preserve the life of the friction plates and gears, but there is enough friction material in the fluid itself that the transmission never slips when driving. (since that fluid acts as the binding agent between friction plates and steel plates)

So when the owner of that transmission decides to do a full system exchange, all the old fluid is gone along with the friction material that was floating inside it. Suddenly, the transmission starts exhibiting a slipping problem while driving, which then puts the owner into a big mess because the only next step is a $2k rebuild. You can't drive around confidently with a slipping transmission and AutoZone isn't going to sell you a bottle of liquid friction material.

However, if you change out a little bit at a time, you are adding additives back into the fluid that help preserve the remaining life of the components in the transmission. There may not be much life left, but the additives will extend their useful life. At the same time, you are not fully draining all the old friction particulate that may be helping to prevent slipping. This gives you a gradual way to determine if the friction plates are so worn that continued drain/fills would be a bad idea, or you might luck out and after 4-5 drain/fills, you have replaced most of the fluid and the trans internals are fine.

So in essence, this is the approach that one can take when one doesn't want a sudden transmission problem to rear its head. A worn transmission is a worn transmission, but if this approach lets you drive it confidently for a few years then maybe it gives you enough time to save up the money for a proper rebuild.

And this is also a big reason why you should try to keep the transmission cool and replenish the fluid additives on a regular basis. High heat (over 250*F sustained) is what makes the additives in the fluid worthless, so try to keep it in the 150-175 range for best life. And regular drain/fills will keep the fluid fresh enough that it can protect the inner workings from excessive/early wear.

 

@Paul123 Hey, I recognize your truck and username! You've answered a few questions I had a while back. Thanks for all your help. You too, @2015WhiteOR

 

Any updates on the issue?

 

Negative. Been super busy. Will update though.

 

take the lower cover off and see if it is louder.

 

Lower cover of what?

 

there should be a sheet metal cover on the lower front of the transmission. This gives you access to the torque convertor bolts. What i am expecting is an increase in the noise level when this cover is removed or something to fall out. You can put a socket on the front of the harmonic balancer and turn the motor over by hand in inspect the flex plate / torque convertor bolts for tightness.

 

this is what I found on my motor swap. The first pic is of the original trans/torque convertor , the second is the original motors flex plate, the third is the replacement motors flex plate... there is an absence of rust on the replacement motors flex plate. I have seen this rust make a "squeek" type noise as they spin. It is probably a long shot but it does happen. Old motor is out of a 2002 Prerunner DCSB 3.4

 

Thanks, @Glamisman. I'll check that out next time I'm crawling around underneath my truck.

 

Did you ever dig around and locate the source of your rattle?