I have used many audio CDs to learn Spanish in the past few years. Sometimes I have heard words ending in "er" pronounced the a slight "d" sound at the end.

For example:

"Ayer" will end with a sound more like "ed" as in the name Edward. I learned it with more of an "air" sound at the end.

Is the "ed" sound some kind of a regional thing? O estoy loco?

Posiblemente loco o no puedo escuchar - ayudame por favor.
In the case of the kind of Spanish spoken in Mexico, int the word "ayer" the "r" sound is very clear it doesn't have anything of "d" Emotion: smile. But, you know? lot of children can't pronounce the "r" and instead they say a "d", also some adults with speech problems can't say "r" well.
Yes, it's clear but it doesn't have a strong sound when it goes at the end of the word, maybe this is your problem. The sound is softened in this position.
It was really on one set CDs that the "d" sound was very noticeable. Much of the time I hear a slight hint of the "d" sound.

Muchas Gracias

por fin es la fin de semana