Intermittent Engine Rattle (cannot duplicate consistently)

I have a 06' 2.7 Manual 221k miles. The noise does not seem to care if the engine is cold or warm. It also is not consistent. Sometimes it happens, sometimes it does not even when I'm trying to recreate the sound while parked in neutral, with or without the clutch in, revving the engine to specific RPM each time (1500 to idle, 2000 to idle, 2500 to idle). When I am able to recreate the sound while parked, it will happen at a different rpm each time or it will fade away the next moment I push the accelerator. The sound seems to be coming from somewhere in front of the dash on the driver side, it will sound between 1,500 up to 2,500 rpm when just revving the engine but only at the moment the engine begins to throttle down, other times I hear it while in first gear for an extended moment (like low idle mph leaving a redlight and making a turn maintaining a certain RPM level). When the truck is moving I only hear it while in first gear if that makes a difference.

I also have an intermittent low idle that, happens from time to time, but does not match the same occurrence as the rattle. Engine usually idles around 800-900, but will occasionally dip to 550-600 rpm. I will rev the engine just to see of the idle speed picks up, but again sometimes it does sometimes it does not during a drive cycle. The sound makes me think of something rolling/rattling in a plastic box, but I'm pretty sure it is not my cabin air box. Recently did an oil change (5w-20) at 200k and nothing appeared out of the ordinary with the old oil. I've researched the existing threads here on the timing chain, OCV, and VVT related problems, and while I have not eliminated those issues, none of the posts seemed to share what I have going on exactly only due to those individuals stating their rattling was constant and at cold start. Mine is not dependent on warm or cold engine, nor constant when it does occur.

I am checking the codes today and will update. But if anyone has a serious suggestion I would be interested. Thanks in advance. Cheers

 

I have the '05 4.0 which was known for HG issues so hopefully this isn't the case with you, but you might check the head gasket. in my case, it sounded like a few bolts or coins loose behind the dash in front of the steering wheel -- I'd notice it up until the truck warmed up and really only when going from a stop to a start or revving. Hopefully something is just loose and rattling

 

Might sound stupid, and doesn’t really sound like this might be the issue, but have you checked the heat shields underneath, and your U-Joints? Just an idea, like I mentioned above, most likely isn’t the issue, but I’m just throwing things out there.

I had a rattle that came from what sounded like the front passenger side/under passenger dash/firewall area every time I got to 35-44-55-ish; ended up being my U Joints. Makes sense because I’m nearing 200k miles, and still had the original OEM joints. That and a front passenger wheel bearing change, and my baby doesn’t make a single noise anymore.

 

No Codes were being shown yesterday. Thanks for responding. The head gasket did play through my mind a little. It just seems to be something different though. I have been keeping an eye on coolant level and oil appearance, and all seems well on that front aside from the some oil consumption (about 1/2 quart every 1000-1500 miles). This was going on before the last oil change I might add.

This week, for example, I heard the rattle/gurgle Tuesday and Wednesday. Thursday and Friday nothing until last night I had just backed out of a parking spot and when I put it in first and clutched out I heard it, but not again after when i sat their for several minutes while a buddy of mine was listening to me revving the engine as described in my OP. He told me I was crazy and hearing things. I know it's hard to describe things just saying "it's making this noise" but the sound i guess more like pouring out a water bottle that I hear but also feel in the clutch pedal and the steering wheel and the sound seems to be distinctly from that area. Is their something behind the gauge cluster that is dependent on engine speed that might be acting up?

 

the heat shields I have not thoroughly checked. There aren't that many honestly on the 2TR engine, and all the exhaust shields are on the passenger side.

 

Hmm, I’m not familiar with manual models, but only other thing I can’t think of that I don’t think I mentioned in my previous post is your carrier bearing. As I mentioned before, the sound seemed to come from the same region as yours, so it could be misleading in that matter. Maybe take a look around your torque converter, real main seal for any slight leakage. Also has happened to me, where I had an extremely slow leak from the rear main seal and one day my truck just started to gradually shift weirdly, and got progressively worst, due to it finally getting below the minimum trans fluid needed.

Sorry, i can’t help more. I just have no experience with manuals enough to even guess anything further without risking looking like a complete idiot.

 

Harbor freight ...stethoscope... $15 ... my vote is for the throw out bearing

 

The throw out bearing has been making its noise since I've had the truck in 2008. The concerning noise has gone away now for the most part but I am worried something is still amiss just based on the engine's sound and character. Vibration seems more noticeable, the idle seems rougher, and maybe a slight decrease on low end power. Had a misfire about three months ago where the #1 coil cooked itself and the spring wire inside it basically arc'd itself to death. Replaced with new denso coil and sparkplug, and ever since then that's when this rattle and engine idle vibration was noticed. The motor mount is legit concern, but I don't know how to check if its broken other than just looking for obvious damage (cracked metal or broken bolt)