Scarlet, I just posted in another thread that exercise - demanding exercise - elevates the heart rate as you know... but sometimes the resting heart rate is still elevated the next day. This could be what you are noticing... that your "normal" heart behaviour is just a little different.

When I have ridden an individual time trial well (intense exercise), my heart rate at resting is about 4-5 beats above "normal" that evening and still remains elevated 2-3 beats by the next evening.
That evening of the TT I can definately "feel" my heart beating/notice its presence" much more than after moderate exercise/riding.