Is it a 500 or a 505? The filter section is the same but the 500 is much older, the 505 replaced it 2009.
What type of filter material are you using? It should be filled with a 0800.010 cartridge or a 0800.140 foam sponge or a 0870 with carbon/chem media or a 0871 with floss. If you are just putting floss in the bell, especially if it is not a good quality combed filter floss, like Eheim or our macro or micro wadding, that will clog very quickly, their is no way for the water to get around it and through the bell, once the bottom gets dirty, the filter is clogged. With the 0871, the water goes in freely and can go through all sides of the filter wadding.
It is also not uncommon for the finer media to clog in 2-4 days if the tank is dirty, it just needs to be changed or you can use the 0800.140 foam sponge which is coarser or the 0871 filled with our macro wadding which is a coarser floss.
The bubbles are caused by the clogged media, a vacuum is generated by the pump since no water can pass through, the water is basically boiling from vacuum pressure and the dissolved gas is escaping.
I suspect that either the media is not correct or not in the correct cartridge or the tank is dirty and media will need to be changed frequently or coarser media used until the detritus is removed.
I use a 3167 at home and if I stir up a lot of detritus, I can clog a 0800.010 in 2 days, which is not unusual as it filters almost as fine as a diatom filter, I just change them out until I get all the dirt out. Once the water is clean, the cartridges usually go a week or two.