I just recently put a quieter exhaust on my 2006 Mustang and now I’m hearing a bit of a hiss from the transmission when it is in Drive or Reverse. I’m neutral or park, it is totally quiet. I’ve read in some older posts doing a search on google that others talked about this and some said it was normal and others said they have no noise. It’s especially noticeable in a drive through or in my garage (with the windows down) where the sound probably has something to bounce off of. Any ideas, or is this normal?