Strange 308QV Engine Noise - Any Guesses

I have an 85 QV, whose motor was rebuilt in the last 300km, and am getting a strange sound that I am not sure if I need to worry about. It is a "moaning" sound that happens under 3000 rpms, and seems to get louder as the engine warms up. The moaning is nearly identical as the sound that a power steering pump makes, when it has a ton of miles, low on fluid, and when the steering wheel is turned all the way to one side (I know you've heard this before!). It is not resonant, and its pitch rises & falls with engine speed. I cannot seem to locate its source with either a mechanic's stethoscope, or a low-tech "hose-stuck-in-my-ear" tool. I do know for sure that is is not coming from the valves, intake plenum, water pump, or timing covers. I know that describing sounds is difficult, but I was just wondering if someone might be able to identify with this sound before I dig too deep. Coudd this be coming from the alternator?

 

Well, I don't hink it would be an exhaust leak, because its requency seems to high for that. I'm guessing that around 2k rmps, it is putting about a 2kHz moan etc...but since you mentioned that, could it be the air-injector ports/holes where the 4-to-1 tubes connect to the heads? Like a whistle?

Hmmm. Interesting possibility which makes loads of sense as to why it would sound like a power-steering pump airating fluid. I get oil pressure instantly, but it seems to fluctuate quite a bit between idle & high rpm states. Since it was a total engine rebuild, I have replaced my filter 3 times in the last 300km to flush out any "crap", and sound persisted with all 3 UTI filters. Could I not be getting a perfect seal between the oil sump tube, and sucking air in there? That woudl suck (no pun intended). Where else could air be introduced into the oil flow? I'll have to put my stethascope on the oil filter & oil pump location to see if I can hear anything.

 

Thanks for the great suggestions. After a nice long drive today, and after pulling back into the garage, I continued to try to hunt down this source of this minor annoyance with my stethascope. I FOUND IT and it surprised me. When I put the probe on the hose which runs from the air-injection vacuum switch to the air filter box, I could hear it loud as a bell. My one-way valves are new, and I did test the operation of the vacu-valve when reinstalling it. This exhaust air system just seems like a nightmare pain in the hind quarters. Any suggestions?

 

I ran across this thread and thought I would post a follow-up to doccument what this problem actually turned out to be, in case anyone goes as nuts as I did trying to figure out what was causing such an annoying noise. This was actually due to haivng one of the "defective" oil coolers on my car, and this problem is pretty well doccumented in other threads. It is a whining noise that varies with rpm and sounds really loud in the cockpit and goes away at very low & very high rpms.

I was misled to thinking it was coming from the air injection system because the hose (that runs to the airbox) was touching one of the oil cooler lines. I just didn't think such a noise could come from an OIL COOLER, but when I finally touched my scopes probe on it....it practically blew my ears out.