I own a 1991 75000 BTU Ruud furnace. Every now and then it booms and flames shoot out the front of the furnace when it starts. I have had it cleaned and had the thermo couple replaced it seemed to help for a while now it back and seems to be worse. Any suggestions?

I suggest you call a the HVAC company back to correct the problem. Something is definitely wrong and the problem needs to be addressed now not later.