It could be one or more of your HDMI cables. I had exactly the same issue with my PS3 and TV. For 8 months, I thought there was something wrong with my AV amp as I was getting random dropouts as you describe.
It wasn't until I moved my PS3 upstairs to connect to my PC monitor and witnessed the same dropout, that I tried a different HDMI cable. It stopped the dropouts immediately.
I since ordered some better quality cables and have had no issues since.
Hope that helps