Rattle sound when a/c on

I'm noticing a strange rattle outside the truck when I'm running my a/c. Any ideas or is that normal? Truck is running fine and a/c is working.

 

Compressor or bearing?

 

Can you hear the noise inside the truck? Where exactly outside the truck does it sounds like it's coming from?

The front of the engine is most likely a bearing in the compressor or the compressor clutch like @TegoTaco suggested. If it's coming from the passenger side near the windshield then it's probably the blower fan. Pull the cowling off and stick a shop vac down the fresh air opening and suck out everything you can. Then pull the glovebox and check your cabin filter. If it's missing, for some reason, a twig or leaf couple be running on the fan like a card on the spokes of a kid's bike. If the filter is clogged bad enough, it could have sucked in and be doing the samething.

 

Can only really hear it outside. Pretty sure a/c related since it will only make the noise when I turn on the a/c, goes away when I turn off. I'll check out the compressor. Thanks

 

Pop the hood and start looking around at everything that's connected to the serp belt.

If you have an infrared thermometer pointing it at all the bearings and looking for one that's running hotter than the others will sometimes reveal a problem.

 

Literally sounds like something is loose and rattleing around.

 

Bearings can sound like that sometimes, so can the clutch. Maybe some debris in your fan assembly and it is hitting against the firewall.
You need to narrow the component the sound is coming from. Engine Stethoscopes are available from HF and auto part stores, cheap and helpful at times.
Or you can use a rubber hose to direct the sound to your ear. I know, sounds strange but it works.

Either way, please post what you find so this thread can be a resource to someone.

 

Had the same issue but on a Sonoma for 75K miles. It was the load the compressor put on the engine that made something else rattle under the truck. Weird thing was if I pushed the clutch in, it went away. Never did figure it out but the A/C could still freeze ice cream when I finally sold it on after 13 years. [it was a 98]

 

My A/C is making a kinda humming sound for a lack of a better word . You can hear it in the cab and by the grill up front. You cant really hear it when in drive . But I can really hear it in park . It only dos in when the compressor kicks in. It is cooling fine just making that humming like sound. I took it to a shop and the guy said that he though it could be the compressor but was not sure . So under warranty he changed the compressor with no change to the noise. Not sure what to think at this point. I have a 2011 with the 4.0

 

Ok, I am having a similar issue after a bad oil leak/cleaning the engine bay, likely ruined the seal. A/C blows cold (42!) and the rattle sound happens when the engine is hot and/or when the a/c clutch is engaged. Essentially when there's a tad bit of extra load on the belt. Can induce with power steering as well. Engine runs fine, then under a/c load, rattle is constant. Load stops, so does rattle. I have it isolated to the clutch assembly area with a mechanics stethoscope. The sound is coming from there. Pulled the belt, wiggled all the pulleys, everything feels fine, so ...another finger pointing at the a/c clutch assembly.

So here's the rub. I KNOW its the bearing, but you can only get the clutch assembly. Has anyone replaced JUST the bearing on a 4.0L and what's the part#??

Had a local Toyota only garage look at it, and they only replace the whole compressor and clutch. This is like a $30 part max, never imagined it'd be this elusive.

 

Same indicators as kasnerd, very inconsistent tick coming from lower passenger side of the engine bay. Only occurs with the ac on, id like to assume ac clutch since it isn't constant. Going to stethoscope the area this weekend.

 

Belt tensioner was bad, so was the clutch. Replaced the idler pulleys at the same time and a new belt. All good.

 

Still haven't got around to it, but ill definitely keep that in mind as I'm diagnosing, thanks for the info.