99 Ski Nautique muffler

Hi all, I've just got back from a weekend ski-ing boarding etc, whilst running at between 15 and 25mph there is a loud droning sound, if you lift up the rear centre floor section and put pressure on the muffler it appears to get quieter, over 25 it seems to all but go away.
Is there anything that can be done? my suspiscions make me think that perhaps something has fallen apart internally. The hoses are not fouling anything and the self adhesive neoprene that the muffler sits on has been replaced.
Can the muffler be cut open and the baffles be re-glassed?
I need to sort it as my ears are still ringing 4 hours later.

M3Fan wrote: There is supposed to be foam padding under the muffler. This tends to dislodge over time- check to make sure that it's still there.

I have replaced that with new, no difference.

No it hasn't always done it, I haven't had it long and it was as sweet as a nut when first purchased and tried, however on my first launch i did hit the concrete slipway with the prop and bent 2" of every blade at right angles, I had it repaired but no-one seems to be able to deal with cnc machined props here in the UK. I have checked the shaft and all appears to be ok there and have had the prop repaired but as to its state of balance after the repair i can't be sure. A dealer over here has told me to put my arm down the inlets and outlet of the muffler and check the baffles as he seems to think this is a common problem and if so can be repaired through the holes.
I can get a good deal on a new Acme 422 from a dealer friend who use these props on their home built tournament inboards so will go down that road as well, come the weekend i'll pull the muffler off and have a look.
I'll keep you posted

I'll pull the prop and put a dial guage on the shaft at the weekend and see what i find.

100% chances your shaft is bent at some point....
It takes a small hit to bend this things..been there a couple of times...