i just got turndowns on my truck last week and sometimes when i stop at a stop light or stop sign or put it in drive or reverse it seems like it vibrates and makes a vibrating noise. and it dont really sound like its an exhaust leak but i dont know. but it never does it driving and i dont think it does it when im in park. and it isnt constant. it will start and quit them start again sometimes while im stopped at a light or stop sign.. and it seems like its the exhaust but i dont know. what do yall think it is? is it a big deal or what? please help.