...รถแก่ๆ ไป เครื่องล่างดังโคล้งๆเคล้ง แต่ไม่มีเวลาไปเข้าอู่เสียที...

If you are driving such an antique car (rear-wheel drive - with a power axle; like mine), it is very likely that you have loose or worn-out universal joints on the axle. A way to test is to let the car roll downhill in neutral if you only have noises when in gear but quiet in neutral -- the bad news is it can be hard to find the right universal joints.

In front-wheel drive cars the problem is usually much worse. There are usually noises whether in gear of not.

Better see a mechanic and live to tell more tales rather than to end up in a ditch -- for a long time.