[nereids]

Sounds like the knocking noise is coming from the blower impeller (not the blower on the heating element.) Is the impeller supposed to rotate freely around the shaft of the motor? When the impeller is rotated by hand the motor shaft does not turn. There seemed to be too much play around the shaft. It's made of plastic so maybe the part is just worn and causes it to wobble. If the impeller is not tight around the shaft I don't see how it impels any air.

[denman]

Here is your parts breakdown
Maytag LDE8414ACM

The blower wheel should be tight on the motor shaft
The clamp could be loose or off, since it has been loose for awhile the shaft hole in the blower is most likely messed up so you may have to order a new one.

If you click on the picture or part number of the item of interest a new page will open often with better views and help from others who have used that part

Here is a service manual which may come in handy now or in the future
http://www.servicematters.com/maytag...s/16008714.pdf

[nereids]

I found the solution before any replies. The impeller was broken where the shaft goes thru. I went to a parts store, described the problem, and they knew right away that the impeller was broken because it did not rotate with the motor shaft.
Luckily they had a new part in stock so I did not have to order one. Installed the new part and everythinig works fine.