Is it like a whooshing heartbeat sound or more of a high pitched ringing or buzzing?

If a whooshing heartbeat sound it could be a bruit.

If you have tight neck muscles - scalenes or SCM - those might be clamping down on the arteries or nearby tissues in the neck , causing the heartbeat sounds..
It seems to be in your ears it really isn't.

You may even have trigger points or muscle spasms that are a partial cause..

I had severe neck muscle spasms and heard that sound constant for months until I happened to come across a chiro that was very well versed in trigger points & spasm. A very good PT should be able to help also..if you can't locate the issue on your own or with a friend to help.

trigger point info-
http://www.triggerpoints.net/symptom...-shoulders.htm
http://www.pressurepointer.com/pain_reference_chart.htm