I have not fixed my washer dryer combo as the problem with the random 3 beeps seems to come and go just as yours used to do. For months it was silent but now it's acting up again.
What I have figured out is this: my machine's has a designed-in 3 beep pattern that occurs whenever I initially rotate one of the cycle selection dials when the machine has been sitting for a while. According to my manual, these 3 beeps are to let me know that the machine has been awakened and is ready to accept my selection/command. I've also noticed that there are a couple of different pitches to these beep patterns. For example, when I rotate either the washer or dryer cycle selection nobs, it'll sound the "I'm awake" 3 beeps and the pitch for either of these is identical. But if I awaken the machine by first turning the nob for to activate the fabric softener - which is a separate on/off switch - then the 3 beeps I hear is of a different pitch, and in my case this is the 3 beeps I hear intermittently. So what I've deduced is that I either have a dirty/bad fabric softener switch OR the main control circuit board to which that connects is going bad. Since I'm pretty handy I was was going to dismantle the control panel and remove the fabric softener switch to see if I could clean the internal contacts as well as the external ones - i.e. at both ends of the wires that run from the switch to the main circuit board. Sometimes terminals or contact points can become oxidized or dirty with lint which will cause the affected sensor or switch to become momentarily disconnected and the reconnected which, logically speaking, would cause the machine to 'think' that it's being awakened and this sound the 3 "I'm awake and ready" beeps. I've yet to try this repair as it's been pretty quiet lately but I intend to do it at some point if/when it gets worse.
Now, with all of the above being said, I do not think your problem is confined to just one bad switch or sensor since your beep patterns is random and differentiates from occurrence to occurrence (ie my beep pattern is consistently the same). If I had to take an educated guess, it sounds to me like your problem is either a) multiple switched that are going bad or need cleaning or b) the main circuit board is going bad. If your handy you can try opening up the main control panel (MAKE SURE TO UNPLUG THE UNIT FIRST AND LEAVE IT UNPLUGGED OVERNIGHT BEFORE WORKING ON IT) and then looking around at the various points at which the various switches connect to the circuit board. If there are wire connectors make sure to disconnect them from the switches and the main circuit board and examine them carefully for any signs of corrosion or oxidation. You want to see clean metal wherever contact is made. A little fine sandpaper and a bit of rubbing alcohol (for use to clean the contacts after using sandpaper to remove the oxidized build up) is all you need to clean up corroded terminals. I've applied this technique to many automotive and hone electronic repairs. It always amazes me how so many problems can be attributed to simply bad/dirty/corroded/oxidized contact points.