Bike sometimes gets loud over whoops

[3beejay3]

I have a 2012 GG 250 XC ES with a bit over 90 hours on it.

It's bone stock except for hand guards and rad braces. Lately it occasionally will get quite noticeably louder when hitting a large whoop or hummock at speed. Then, when I hit another one a few seconds to a minute or two later, it will return to stock noise levels. Which are about 88-92db
It's noticeable enough that other riders nearby can definitely hear it, I'd guess that it gains about 10-15 db.
It doesn't do it every time, but maybe 3-5 times on a long days ride. (it actually came in handy last Sunday during an enduro, as it happened several times co-incidently when I was closing in on a slower rider, making them aware of my presence, then would quiet down again soon after I passed them - weird......)
There isn't anything loose externally on the exhaust, I've checked several times.

Any thoughts on where to start looking? Power valve? Silencer?, ??

[Jakobi]

Sounds exhaust related.. is it possible its pushing off the header a little? Any signs of spooge anywhere on the exhaust? Internally, has the muff been repacked? I wonder if it could have a crack or the likes inside?

[3beejay3]

There has always been lots of spooge out the exhaust, since new, both out the tail and at the joint where the expansion chamber and muffler meet. (I haven't bothered to properly jet it)
The muffler hasn't been repacked as of yet.

I'm suspicious that something occasionally comes loose in the silencer or sticks in the PV. Although when it gets loud, it doesn't seem to change power delivery characteristics.
Another possibility is that maybe the subframe is sometimes allowing the joint to pull apart......??
Wondering if someone else has had this problem. A search didn't bring any results for me...

[gasgasman]

Common problem when the power valve actuator is loose.

[Boom Boom]

Sure sounds like the PV sticking.
Mine would do that when I hit a log hard or other impact.
Serviced the PV and no longer does it.
My PV linkage had a bunch of play that also needed removed.
Not sure if the cleaning or snugging up the linkage fixed the problem.

[3beejay3]

Ok, will check the PV

Thanks.

[forgiven]

PV sticking. I went to the Maxima K2 just for that reason. I loved my 927 but spooge and lots more cleaning facilitated the shift.

[Clay]

Sounds like the packing is suddenly blown out of the silencer and then returns to normal?
Power valve.

[andykr87]

My brother and I's bike both did this but they would lose all low end then come back on = stuck power valve. Some of the power valve bearings on both our bikes were bad, two on the water pump side and one on the other i believe. Its a super common bearing (6505 i think).

[Jakobi]

I had mine stick open once at 150hrs. Major loss of bottom end and sounded more like the bottom end was toast rather than just louder. Bearings are the same as the rollerblade wheels I found mine would lock occassionally and replaced all. Sometimes a bit of carbon on the drum valve of the PV can jag against the cylinders internal casting a bit too.