Noise on 99 K2500 Suburban

[Guest LeeR]

I have a 1999 K2500 Suburban with the 7.4L engine. Sub has approx 62,000 miles on it. Just recently I began to notice a loud "vacuum leak" sound coming from the front passenger footwell area. I notice it mostly when the vehilce is cold but it is there more or less all the time. When I start up the sub and place it in drive the noise becomes very noticible. Then upon acceleration the noise becomes even louder and the sucking or vacuum noise increases as more throttle is applied. To me it sounds like a large vacuum leak under the dash in the area of the passenger footwell. It did not use to do this and my friend has the same suburban and his is completely quite. My local mechanic told me it was the air intake and the fact that I was using a K&N filter. Over the weekend I took the air intake box out complelely and just installed a paper filter to the inlet duct. I drove it and the noise was still there so I at that point made the conclusion that it was not related to the air intake.

 

Can you help me figure out what this is ???

 

TIA

LeeR

[GM-Tech]

Noises can be among the most difficult problems to find and fix when it is right there in front of you. Trying to do so over the internet without hearing it is probably nearly impossible unless it was a common issue we see a lot and this is not familiar to me.

 

My first suggestion would be to look for an opening to the engine compartment. In otherwords, a grommet or some such that is supposed to be there but has been pushed out of place. We rarely see that on the passenger side, but it's not too uncommon on the driver's side. Especially on a vehicle that has had aftermarket equipment installed. The installers often take the easy way out and just push a major harness gromment out of place to run their wires through and then just leave it out of place. LOTS of engine and road noise comes through.

 

I'd also look for a low coolant level which can often cause a rushing or vacuum type sound in the heater core. The coolant expands some when the engine warms up, so if it's just a tiny bit low, perhaps that change is enough to eliminate it when warm.

 

That's all I can think of offhand.

[Guest LeeR]

I did look under the hood and under the vehicle for holes, grommets missing or having fallen out etc etc - in other words "openings" in the bulkhead and found nothing out of place - my guess is that it is a vacuum leak (either a loose hose or a failed hose releated to the HVAC. It however does sound like the exahust noise is right in the footwell area - a mystery to me. But certainly wasn't there a few months ago - something has changed.

 

thank you for your help - if you have any other suggestions I would greatly appreciate it.

[GM-Tech]

When I start up the sub and place it in drive the noise becomes very noticible.  Then upon acceleration the noise becomes even louder and the sucking or vacuum noise increases as more throttle is applied.

 

All the actuators for the front AC/Heater are electrically operated, not vacuum. Besides, vacuum noises increase at closed throttle and disappear as you accelerate and manifold vacuum drops. So if your noise is becoming louder on accel, I don't see it being a vacuum noise.

 

I still say possible heater core noise. You could try clamping off one of the heater hoses temporarily to prevent any flow through the core and easily eliminate (or verify) that as the cause of the noise.

[Guest LeeR]

I dont know what I did yesterday evening but all the noises are gone.

 

I am baffeled but very happy that it is quite again

 

Here is what I did do though-

 

1. I pulled up the carpet on the floor board to look under it, finding nothing I then simply put it back

 

2. I removed the glove box and looked inside the dash area and found nothing

 

3. Under the hood there is a black plastic cover that snaps into the side wall where the antenna wire is routed - since it is always falling out I taped it in using electrical tape.

 

That is about all I did. This really has me scratching my head (almost bald in that area) but Like I said I am elated that it has stopped.....