Lost the exhaust tone??!?

[LOK[R9]]

Ok ... I was driving to job last night, riding at 120 (kilometers of course :P) as always when I downshifted to fourth to keep my speed even while in a hill. (you those damn 106hp motor .. no damn power on fifth :P) So then POUF! No more exhaust tone .. stock sound. What causes that?????? I mean the exhaust dont seems to have loosen or lost any part but it's not sounding the way it does.

I'd appreciate any ideas of what might be the problem. BTW I have a Apex'i WS ... great purchase but I hope it had no flaw!

[99civic03]

I know the Apexi WS is one of the quieter exhausts, but I dont think it should be doing that, Id have it looked at by a shop.