Undiagnosed Macbook Pro Issues (freezing, kernel panics, alarm)

My 2011 macbook pro has been giving me trouble for several months. It started having trouble going to sleep, having repeated kernel panics, freezing, 3 beep alarm sound more and more frequently. I took it in several times, and never got a solid answer about what was wrong. Replaced a supposedly faulty stick of RAM, which solved the problem for a while, but then had repeated issues of the same kind. Now it's working in spurts, occasionally freezing. Is it time for a new machine? What could this be? None of the hardware tests detect any problems. I'm at a loss.

3 beeps is a ram problem if only one stick was replaced the other could have died even the replacement could be bad .
If you want to check this for yourself you can remove one stick and then try it if it works move the same stick to the other slot just to rule out a bad logic board or ram slot connection.
If under Apple Care I urge you to let Apple perform the fix.

Also curious, where did you take it to? Apple store or independent retailer or non apple repair shop?

I took it to a non-apple retailer. Also, 2 days out of the box 2 yrs ago, it died and I had to replace the logic board (luckily it was still under warranty). Now it's not, so I'm hoping for something less serious.

If the RAM slot and not the stick is bad, is that an expensive fix?

Probably since it will require a logic board replacement.

the 2011 did have a known issue, which Apple is covering for longer than usual..

IMHO, It's worth taking in to an Apple store and have them look at it...

I saw elsewhere on this forum that they did a 3yr extension on certain of the 2011 Macbook Pro's, but this is just a guess......