Lifter & Valvetrain Noise - IS THIS NORMAL?

I've had my 2005 LR3 V8 since it had 12K on it...now I'm around 35K.  Since I purchased the vehicle, it has sounded like a 1975 Ford Pick-up truck...lots of lifter noise, almost sounds like a leaking exhaust manifold.  Most noticeable at lower RPM's when you are in town or next to a building or wall when the engine is under a load.  I frequently tow a 5,000 pound boat, and the truck really sounds bad as I drive through my neighborhood & through town.
 
Anyone else notice this noise?  My dealer says that it is the mechanical lifters on that engine, but it still seems excessive to me.
 
Thanks in advance for your help!

Just did another post on this same issue . the valves are adjustable and can be inspected for clearence, I'm not too sure if its considered a maint. thing or not. if it is you might have to pay for an adjustment and if it is nessary the cams will need to be pulled to access the shims, big job !