[TenTec] Omni V - sidetone/headphone problem?

[james murray]

Picked up a nice used Omni V and very impressed with it so far.  One problem I came up with is that when I put the headphones on the first time the sidetone rattled my eardrums a bit.  In order to use headphones I had to turn the sidetone all the way down.  When I pull the phones out sidetone is barely audible.  Headphones are 
Yaesu YH-55, 8ohm.  Manual says 4-16 ohms.  Any ideas.
tnx,
Jim/k2hn