Was using my TTHP today and while cutting it developed a vibration when blade is engaged. When blades are off runs fine. I have checked; Blades, no nicks and balanced. Pulleys above deck seem fine, loosened belt and all seems ok. Looked at pulleys at rear of mower and they look ok and don't feel loose. I don't use this mower but about once per day, my primary is a 52" Lazer. The tthp only has about 50 hours on it. Thursday, I need to use the mower for two jobs so your help will be greatly appreciated.