m1950

when at idle in drive my car makes this sqeeking and knocking sound the knocking sounds like it is comming fron under the driver floor board and i can feel it knock in the brake pedal.when i rev the rpms the sound an knock stop until it gets down to idleit also does itwhen im coasting. this doesnt happen all the time it comes and goes however my idle is choppy when this is happening almost sounds like i have put a cam in it you know that lope sound. it runs rich i havelt hpipe &mil elim on it but gas milage is S**tty but when it is running good its nice