I never worked on the Alex but did work on the Reflex which was basically the Alex with MIDI support added. I also don't have the Alex service manual so I can't look up the codes.
That said, I don't think a bad SRAM would cause the problem you are experiencing. The SRAM is used by the main processor to store variables and other operating system type things. If the SRAM was bad, you probably wouldn't be able to select programs or otherwise interface with the Alex.
Pulsing noise usually comes from either a bad DRAM (used to store audio data), a bad op amp or power supply. Question: does the sound of the noise change when you change programs on the Alex? If it stays the same, then it's probably NOT the DRAM, which is good news. Bad DRAMs also tend to sound very harsh. Op amps tend to sound like a constant hum. The fact that it's pulsing, suggests to me that maybe one of the large electrolitic caps in the power supply has gone bad. You can sometimes even see them bulging. They are the large round capactitors near the middle of the board. I believe they are 1000uf parts. A nice thing about these parts is that when they go bad, they just go open so you can just solder another part in parallel with it to see if the problem goes away. You can also use parts with a higher voltage rating if that's all you can get your hands on (i.e. Radio Shack). They should probably be 16V or higher but look at the part to be sure.
If the part is bad, you'll need to pull the old part out and solder in the new one. These can be tricky to desolder since they are often connected to a large ground pad. I usually alternately heat the pins with a soldering iron, rocking the part back and forth till it comes out. You then need to clean the holes out with a solder sucker or solder wick.
If the problem is an op amp, it really requires an oscilloscope to find. Replacing them is pretty easy however and the parts are pretty easy to find.
I hope this all helps. Good luck.