The impeller change on these is pretty easy. Find the shift rod connector (one long nut and a jam nut) at front of lower end and disconnect then five bolts for gearcase to extension and gearcase slides right off with pump housing fully exposed.
I refuse to even do these without the full and complete kit Honda sells. It comes with everything you need to do a good job ie: impeller with housing and seal, new drive key (VERY important!), friction plate and gasket as well as a new water tube connector and new bolts. I tell my customers that if they pony up the cash now for this kit, they can cheap out and just buy the impeller and drive key next time since we know it's all fresh. They're already "saving a buck" using my cut rate services so if they don't want to do it right, they can do it themselves. You can make up your own mind. Just make sure that you look CAREFULLY at all those parts before you decide. Use plenty of assembly lube to prevent dry start.
One thing that doesn't come with the kit is a little seal that sits on a gusset in front of the pump assembly. It is called a "water grommet". I suspect that it is actually a pad for helping to quiet harmonics coming from the gearcase but I'm not sure. It's there, you'll be there, so why not change it?
If you are concerned that something is happening under the flywheel to make that noise, then you will need to remove it to take a peek. I can tell you this; it is a taper shaft with a key and it comes off HARD. I use an impact gun with a Snap-On wheel puller to get them off and there is always the danger of one cracking. Haven't broken one yet but...
If you do decide to go that route, make sure that you leave the flywheel nut threaded on loosely so that when she comes free, it won't shoot out into the street or, worse yet, hit you in the mug.
Try this: Unbolt the three bolts on the recoil starter and, leaving the cable attached, just lay it out of your way. Get a section of coathanger and use it to probe up under the flywheel for the big washer that is used as the timing belt guide and retainer. If you can detect any movement of that washer then the nut has come loose and you need to get that resolved asap. Honda makes a hard as nails crankshaft so it is probably ok but you will need to replace the timing gear, belt guide, woodruff key and retainer nut.
If you don't find the washer loose then good but...You're noise could still be coming from up under the flywheel. Something else I've found lately on a couple of '03
BF8D's is the delamination of the charging and pulsar coil insulation. It gets dry and brittle and starts to peel. I just use sterile gauze and shellac to re-wrap them when I find that. I never associated any noise with these but I guess it is possible that a piece has come loose and is rubbing the flywheel.
