Hissing noise on and over 5k any ideas?
 

Hi guys I have a 2005 blob ,it has cosworth panel filter and turbo back decat exhaust, I recently got a down pipe fitted badly and I noticed a hissing noise quite loud when giving it some so I put it down to a leaky downpipe so..I spent a good chunk of money getting a decent downpipe and getting it fitted properly but the noise still persists,I can't see any pipes loose around the tmic area etc but I'm no mechanic I've also had it to a couple of local garage's but tbh they seem clueless,just wondering if anyone has had the same problem or know of any garage local to the w Cumbria area who know what there looking for and could help me out.
Thanks

This sounds similar to my fault anyone any ideas.

Possible up pipe gasket.

I suppose it could be a number of things 😧shame I live in the middle of nowhere..I don't suppose Kwik fit would sort it lol (joke)