Mine does that too. I have removed my intake screen, new high output exhaust, and a smaller pulley probably all contribute to mine boiunceing. I notice once I get above around 20 MPH it stops and settles down. I don't think that it is anything to worry about unless you start to see drastic changes in preassure while stopped or at idle.
Your new exhaust, is it a factory replacement or a performance upgrade exhaust?
BTW: Welcome to the club.