I wouldn't be too concerned about your murmur sounding 'louder' to the Doc....as long as you're asymptomatic and in good health. An echo is a very good idea however (especially if you've not had one recently),as it'll give you a baseline and will show where you 'stand' in terms of the severity of your valvular insufficiency and such. Certainly, a 'loud' murmur can indicate a more significant insufficiency than a less obvious one.
As far as congenital structural abnormalities being inherited (meaning septal defects (ASD,PFO,etc.), ) i'm fairly certain there's a genetic component involved in alot of cases. (i've personally taken care of a handful of such patients who had siblings or other family members w/similar problems)
When speaking of 'leaky valves' (the benign variety), I'm not certain. They're fairly common and i don't know if they're passed along genetically??(good question for your doc...my gut feeling is no, you shouldn't fret about this...)).
That being said, a 'leaky' AV d/t a missing 'flap' isnt the 'common' variety of benign murmur. Again, good question for your doc. ...(now i'm curious...i'll be asking a doc as well!)
PS: As far as sleep studies, last i heard they're somewhere between $70.00 and $70,000.00 . ..(I'm not sure where exactly).