Here is a link to a parts breakdown DLB1550 Parts List
Try to narrow down where the squeak is coming from
You will notice that you have a center mounted drum
This is a common area for noise
The high temp grease used on this bearing dries out over time
There is an access door at the back of the dryer
If you feel this is the culprit
Open it up and put a little oil on the bearing, do not use too much as you are near the heating element. Does the squeak stop or lessen. This is just to confirm that it is the cause
As far as I know, the only way to properly repair this is to take the dryer apart
Clean and check the shaft and bearing surfaces for wear. Replace if necessary. Re-grease using a high temp grease. Do not go crazy with the grease.
If you have to open it up, I would give it a good cleaning and check ( front glides, belt, idler wheel etc. Also clean and check your vent system. Basically an overhaul.
Other possible causes are motor bearings, idler wheel or front glides ( they call them slides on this dryer) | 
