After budget installed the Y pipe i bought off them whenever i put it in neutral and rev to 4 and let off i hear this metal hittin metal sound almost like " teeet teeet teeet teet "

I had budget look at it the following week and they said its inside the cat and that i needed a new cat.

my question, why would this start right after i put the y pipe on,
and secondly my friend said its the heatshield under the car...
and its loose and when u rev it the y is flexing and hitting against that, and he advised me to get a new one put on or to take the old one off..

this sounds more correct then wha budget said..."its coming out of your cat" when b4 the pipe everythin was fine. Maybe budget did somethin wrong w/ the install and metals hittin metal now.

 

it it's the heatshield, then lift the car up, and have someone ref it up, and actually see if it's hitting it, if it is hitting then bend the heatshield so it doesn't hit. it's very flexible aluminum so it'll be easy to do, if that doesn't fix it, then you might need a new cat

 

maybe it's the "bees in a can sound" from the new y-pipe

 

I had the same issue, try bending back the heat shield around the bracket at the cat / Y-pipe junction. My problems was that this bracket was hitting the area around it.

 

Mine sounded like it was coming from the front of the car, but it was actually the exhaust piping hitting a piece of metal that seemed to serve no actual purpose. The piece of metal is immediately before the part of the exhaust that crosses above the rear axle, and doesn't appear to do anything (maybe it woul support the exhaust if one of the rubber hangers broke). Removed it, and no noise since. Try looking there.