Strange noise in 1999 Suburban

I’ve noticed a noise coming from under the dash that sounds like running water or escaping steam. It starts as soon as the car starts up and continues until the gas pedal is applied to accelerate, then it goes away completely. As soon as the gas pedal is released, the noise returns. I don’t think it is related to the brakes at all.

We just had the intake manifold replaced and that’s when the noise showed up. Took it right back to the mechanic and he could not tell me what the noise was, even after driving the car. I thought the noise would go away on it’s own, but it hasn’t.

Any ideas?

My first thought is the vacuum line to the brake booster. Your comment about the brakes makes me wonder…do they feel harder than they did?

Did he recheck his work? I’m wondering if he left the aforementioned line off.

Just a wild guess.

Air Trapped In The Cooing System. The Air Needs To Be Purged.

he just drove it and didn’t recheck the work, but offered for us to bring it back in if the noise continued. I believe at the time he did mention the vacuum line and looked under the hood again, but couldn’t find anything definitive at the time.