G'day,
From your post I gather that the noise you are referring to is excessive exhaust noise, not a grinding noise or such. If this is that fact I would inspect the muffler to determine whether or not it has surpassed it useful life. If you decide it is no good, I would recommend going to you local mower shop and asking if he has a decent second hand one available if you don�t want to spend too much on a new one. You would probably be looking at something like $10. The correct operation of this is vital as it provides a spark arrester, and with out a correctly functioning one a yard of dry grass can turn into an inferno in a matter of seconds (learnt the hard way through personal experience!
As to mulching systems, many have tried and failed. The problem with converting mowers lies in the original base set up and the way the grass is dispersed. Without seeing the base its self it is hard to determine whether or not it is possible, but their is no harm in mucking around (just as long as you don�t injure yourself or coarse.
The one observation I have made with all mulching mowers is they generally have a rounded skirt, which creates a partial vacuum pushing the grass downwards..
Regards Jay
