Panasonic breadmaker suddenly producing loaves that haven't risen properly

recheck the yeast as loaves that fail to rise is a yeast problem

Here's the manual...you may want to review how you are making your bread (have you recently changed any of the ingredients?):

http://www.kenwoodworld.com/uk/products/cooking-baking/breadmakers/bm260-bread-maker-0wbm260001?TabSegment=support

If you use whole wheat flour without any bread flour (bread flour is marked on the bag) you will have small dense loaves unless you add wheat gluten. The product "vital wheat gluten" is for sale in most grocery stores in the baking aisle. If you don't want to add gluten then you will need to use at least 50% bread flour and 50% whole wheat flour to get a larger loaf. Those are the 2 choices to make large loaves using a lot of whole wheat flour.

The loud noise you hear is the belt in the bottom of your machine slipping. You may need to replace the belt. If you are making 2 pound loaves you might want to try making the smaller loaves such as 1.5 or 1.0 pounds. What make and model number is your machine?

Do not use room temp water as the instructions direct. Use very warm water.

Evenly?
If you mean one end is a little higher than the other, this isn't unusual, though, adding more water (20-30mls) may help.

Put this number (310187306476) into an ebay search and it will pull one up. These sell quick so be quicker.

Try 'proofing' your yeast; I've gotten a couple of NON-stale dated envelopes that caused the same problem.
If they are baking through, there isn't likely anything wrong with the bread maker unless the rising temperature is no longer right. During the rest time, feel inside the container to see if the dough is getting enough warmth to rise. 

Falling in middle is usually due to innacurate measuring of liquids. Try again using the instruction manual's recipe and very carefully measuring. Be sure to adjust the liquid if you use honey or other liquid not called for in the recipe.
orleydog

The only thing you can do for these machines is the following:
first, if the unit is always plugged in, disconnect it for at least an hour.  This may reset it.
I doubt there are parts...but if you disassemble the unit and cycle all of the connectors, you may get lucky.  IF parts exist, you'll likely need a timer module.