Well, I am a newbie for ARC AMP. Actually, I just upgrade my system to ARC LS16+100.2. Here is the problem, when I turn the AMP on, there have a subtle "bo" noise come out from speaker and right after ten more second another one.
It is really annoy. I am wondering if this is normal for such HI-END component. My CLASSE CA-100 never have such issue anyway.
When were the tubes last checked? I`ll bet the previous owner said they were "like new".
sounds like you may need a few Tubes, or possibly a checkup may be in order.

call Leonard at Audio Research 763-577-9700

He can hook you up.

Um, guys, the 100.2 is a solid-state amp. When I owned one, I recall that it wasn't the quietest amp upon powering up, but it was normal for that amp.
By any chance are you using a tube preamp? You should always power up a tube preamp and wait a few minutes before turning on your SS amp. Tube preamps often emit strange pulses until they warm up (solid state ones sometimes do the same, but immediately upon turn-on, and disappearing quickly). If you wish to be sure this is the problem, see if you get the same noises turning on the amp while the preamp remains off. Proper power up sequence is front end to amp (CD player or phono stage first, then preamp, then amp). The turn-off sequence should be the reverse.
The 100.2 amplifiers all make a pop sound right at turn on. This is normal. ARC could have gotten rid of this pop but they would have had to make the sound worse and they were not willing to make that trade off.

Your description sounds different from the immediate and single pop that I am describing as normal. You might need to have the amp checked out by a service technician.

Anyway, the 100.2 is a very nice sounding solid state amplifier.

Good Luck.