suprasoup

Hi everyone so I recently developed an odd engine noise from my car. So I can replicate the noise either while driving or with the car parked so it doesn't seem to be load related or transmission related.
So what will happen is if I get the rpms 3k or higher and let off the gas the car sounds like I have an exhaust system ( loud grumble) for like 1-3sec's however my car is all stock except for egr delete. Once its down below 3k it will not do it if I give it gas and let off, its only when I'm at 3k or higher and it only makes the noise once I'm off the gas. Its as if when the throttle closes there is pressure that is being pushed out somewhere or something its kind of like how a blow off valve works give it gas and let off and it evacuates that pressure however like I said I'm stock no turbo so there should be no pressure.

When I pop the hood and give it gas right there and let off it almost sounds internal on a side note my motor is on its way out it has developed a lifter tick and a slight rod knock could this have anything to do with it maybe its becoming loose in the bottom end past 3k on deceleration. It does not happen on acceleration no matter what RPM only on deceleration of anything past 3k RPM.

Any help would be grateful.
Thanks