I bought the Thomas set first. I later bought the Percy set. Now the Percy, is so much quieter when in operation, compared to the Thomas. The Thomas in comparison seems to produce a loud buzzing sound whenever it recieves power which is in relation to it's speed/current. The Percy in comparison is almost silent. I didn't notice when playing with the Thomas set on it's own, but now with the Percy in the mix, it sounds like something may be wrong with the Thomas. It runs fine however. Anybody who has both sets, is this normal, or is something wrong with my Thomas?