85 noise under load

[4hammond]

My 85 wagon is making what I think is a top end noise under a medium load. At idle sounds good no strange noise but does have a slight miss in it every 30 seconds or so. While drive at a steady speed sounds good but under medium acceleration it starts making what sounds like valve train noises (runs good and feels strong) under heavy acceleration the noise quiets down. Motor is stock with 85k on it. Any ideas on where to start?

[BenM]

It might just be carbon buildup. I usually go with some fresh spark plugs and a couple of bottles of Techron in a full tank to see if that smooths things out.

Also, check for loose or cracked vacuum hoses.