I recently had repair done to my wall furnace when the pilot would not stay lit. It still won't stay lit and now produces a loud noise (like a blow torch) when the piliot is burning. Technician says this is how it sounds when they are new and working properly. The furnace did not sound like this when it was a year old.

Seems like the service person increased the pilot orifice size trying to fix the problem. I would look into a possible defective/weak thermocouple as the next repair item to do.