'06 5.3 Yukon XL
~117k miles, just did 'tune up' plugs, wires, fuel system (injector) flush...

intake manifold recently replaced as part of a misfire troubleshooting, still getting p0300 (random misfire) and p0301 (cyl1 misfire) frequently, and rough idle, etc...

Newest symptom/issue... a squeaking sound, roughly 4 squeaks a second at idle, sounds like a belt squeak, but it pesisted even with the serp belt off for a quick (20 seconds at idle) check. Squeak speeds up with engine revs as well... The sound seems like it's near the alternator/cylinder 1

any insights on what this is? Noisy lifters?
previously a mechanic had said he thought it had noisy lifters, but I hadn't heard anything like this, this is new and pretty loud... can hear in the car with doors closed... wife said this sound has been there the last 2 days or so, doesn't seem to go away like I would expect from lifters (but I've never had noisy lifters before, so not certain what I'm listening for...)


Thanks in advance!

 

Possibly a vacuum leak since you say this started started after the intake manifold was replaced.

 

although it started after intake manifold was replaced... there was a 3,000 mile vacation in-between, didn't hear it till last night, so I wasn't necessarily thinking along the lines of causality, interesting.
Are you thinking vacuum leak caused duing intake manifold installation?
I was mentioning it thinking that hopefully would eliminate possible causes, not add to the list of possibilities
Thanks, I'll check PCV and other vacuum lines next time I've got a chance to put my head under the hood...

 

Is the A/C compressor on a separate belt?

 

yes, the A/C is a separate belt... that's on passenger side of the engine, sound was on driver's side. I also tried spraying the belt with Armorall, armorall didn't change anything (which isn't definitively conclusive either way)
Squeak seems to have pretty much gone away, not sure if part of that is the oil I swapped out has 'settled in', so now I'm back to my misfire/low idle and CEL codes.

 

Had a similar squeak on one of my IROC/Zs and it turned out to be one of the bolts holding the alternator bracket was loose.