For quite some time (probably just shy of 2 years) our 45 year old Sears Coldspot upright freezer has been clicking at the beginning of each compressor cycle. It began with just a few clicks a few seconds apart, after-which ran normally until cycle end. Recently though, the start of cycle clicking starts out much more rapid (< 1 second intervals) and continues through the entire compressor cycle although the clicking interval does slow considerably.

I know I should have inspected it long ago, no viable excuses. Anyhow, although I've still not gotten my hands dirty I might solicit some opinions on likely cause. My train of thought is either low freon pressure or a faulty pressure switch. Pretty sure there are other possible factors.

I should add that the freezer still performs its cooling duties and doesn't seem to run any more or less than it has in the past. Any insight as to what might be the likely culprit would be much appreciated.

*EDIT* -- I should clarify that when it clicks it sounds much like a relay clicking off and then back on immediately. A quick "click""click"!