OMG i was just researching Treadmills online and i'm paranoid about the weight limit. I was going for an elliptical machine but the max weight on those were 200-250. I definitely dont want to have to pay $500+ for a machine to hold my weight. So, i found a treadmill for $399 with a maximum weight of 300. I hope it works out fine lol

You guys totally helped me out and were quick, too!! Thanks for the help!!

I bet some of the weight restrictions are to prevent you from suing them if you had an adverse health issue form from the treadmill (ie heart attack)

I am not meaning that to sound harsh either. I just know that rarely do you find a person who is a cross country runner weighing in at higher weights. I also know that anyone can suffer from health issues, heavy or light, but I would think that somethings are just to cover the company's butt.

I am pretty positive, that a walk on a 4 speed will not hurt the treadmill

yeah i agree with ryeb, its probably for a legal reason not functionality limit. These equipment usually have a safety factor built in, i.e the max weight specified is not the max weight it can hold at all. 21 lbs in the context of 300 is only an extra 7% so I wouldnt worry about it.

Yes there has been a lot of good advice given so far. I am a mechanical engineer and if I designed a treadmill to handle 400 pounds of dead weight, I would probably put a manufacturer suggestion of max weight at 300 pounds.
If you were able to get through to the manufacturer or reseller, they would just tell you to observe the original manufacturer recommendations; they are not going to suggest that you exceed those (to protect themselves).

The weigh limit is one thing but the motor is another. A cheaper treadmill (under $1000) is not going to have a powerful motor. If you are using your treadmill and the thing stops dead, and switching it on and off does not restart it, then the motor has probably tripped out on a thermal overload. Let it cool down and you can restart it later, if you're lucky. Try to walk/run along with the motor/belt speed and don't let it struggle to move against you.

(If this sounds like the voice of experience, it is).

I'm really glad my search for a similar problem showed this forum/thread...and this answer! I was sorely tempted to buy a new treadmill for fear of breaking my old one that I haven't used in forever because of the weight limit. It still works, it's just that the motor sounds horrible when I try to use it now.

I think I'll be patient, save my money, and just work on my eating habits first. Hopefully I can start to use my treadmill again soon without any fears.

GrumpyCat a guy I work with had a mechanic come to his home to check out his treadmill, the mechanic did a maintenance type service, cleaned, adjusted, etc. and his treadmill works well for him now. This guy was affiliated with the exercise equipment store where he bought the treadmill. Not suggesting you let a stranger into your home to work on your treadmill, but if you know someone or maybe you could try making sure there aren't dust bunnies nesting in there making that noise or check your manual for things you can do yourself, be careful and good luck