Are you running with a dB killer/baffle inserted? It is quite likely that the "loose" nature of loft insulation (not as dense as exhaust packing material) has caused some, a lot, or all of it to blow out the perforation on the inside of the silencer. If you've got a dB killer inserted it is likely to trap the fibres as they are release through the perforations, partially blocking your exhaust and choking the bike.

I've had this problem before with aftermarket car silencers: Packing material blew out of Magnex back-box on my old Subaru WRX, which caused poor performance, overheating and a melted cat!

Take the silencer off and dB killer out and have a good look through it...

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