hello i need a little help i have a 1995 buick parkavenue ultra and its supercharged too,ok im getting a weird growling noise when i accelerate. but after the car reaches a speed of 20mph it stops,i've tried pressing down on the gas pedal in neutral and park but it only does this in drive.any help or advice would be greatly appreciated

 

Could the exhaust system be contacting anything because of the additional torque on acceleration?
Also it is possible you are getting a resulting vibration from something in the engine compartment itself.