Advice wanted from the tuning guru's

[BikerBoy]

Noticed in the past 2 weeks my Busa has developed what I can only describe as an 'oscillating sound' in 5th gear only, and seems to be irreleveant to rpm but most evident when holding the throttle at a constant position. Still runs smooth and performs well in 5th, but I can hear somethings just not right.

I'm using ecueditor, and it'll be weeks before I can get on a dyno but thought someone might know what I'm talking about and can offer some advice.

Cheers, BB