One of the members on SCn Forum and Vortex with a BT LCR had an issue with wastegate creep, but this had'nt been a problem for many miles, and seemed to occur after a long journey.
Made me happy reading this. Glad my educated guess was accurate.
My own previous experience of my DP flexi having done the same to me back in 2005 was the clue.
Mine did this.. 2.5" Flexi @ the time (crappy pictures back then, sorry)
So if you have something odd like a turbo which does'nt pull or spool as well as it used to or in the case of the LCR tial flexi, a setup which developed boost creep, check out your downstream components, like flexi's (cats) etc - It may be the same for you.