My car has these symptoms too. Monitor your fans and see if they both are working, what generally happens (or happened in mine) my smaller fan failed, which resulted in the bigger fan coming on alot more and much faster and louder, compensating for the smaller fan failure. it always comes on and sounds like a jet! especially when i turn ,my ac on, it didnt do this before. ive orderd a new motor for my fan, costing me £118.