hey! I just bought a bryston 4b-st on ebay, the guy i brought it from said its still under 20 year warranty, whenever I turn it on it works for a few mins and then all of a sudden all i hear is high frequency range, so if i Turn it off for a few minutes and come back its work fine all of a sudden and then a few mins later it stops, I kept playing with it and sometimes i hear clicking noises from the bryston and then i don't hear sound again... weird issue, does anyone know why its doing this? and how I can fix it or get it fixed? I'm using it with ProAc speakers. please help