My free standing home freezer (Spectra, 1400 liter) started to make a loud humming noise. I assumed that the compressor was vibrating and fixed that problem just by adjusting the height of the adjustable front legs. I left the unit unplugged and open all night to remove some frost and do a good cleaning inside. BUT, a few hours after I restarted the freezer I opened the door it check if was cooling. It was. I closed the door and then heard a bubbling/sizzling sound. Something like bubbles escaping from a hole or sound of hot cooking oil when you drop a small bit of food in. The sound lasted for a about 5 seconds. During this time, the door would not open (yet I do not believe that there is any locking mechanism on this model). Eventually I was able to open the door. Each time I opened the door I heard the bubbling noise and each time I could not open the door for some seconds. Also, the compressor case feels hot to the touch, but perhaps this is just because it is working so hard to remove the all of the heat (the unit was off for 8 hours). I can not keep my hand on the case for more then a few seconds. Is this normal?

Any ideas what is this bubble noise? How to fix that?

First off, hot compressor? Yes that is normal. It should become too hot to touch, but not so hot as to be a fire hazard. Sounds like it is fine.

Buzzing noise, hissing, sizzling - these are common descriptions for the noise from the defrost system. As water drips on the defrost heaters they sizzle the water.

If it is cooling okay, then I'd rule out a coolant leak from the coils.

Re: door not opening, if you adjusted the front height adjusters, you will add a couple more pounds of resistance to the door opening. Also, if you close the door and then immediately try to reopen it, you can get a small vacuum force holding the door closed. If it isn't persistent, I wouldn't be concerned.