Infernal Cables!!

A small magnet on the end of a 5mm allen key is perfect for internal cable threading.  Done in no time at all.  Pop the combo into the frame and thread the cable through until the magnet picks it up.

Might be worth getting new internal guide tubing too, PTFE F4 Tubing Pipe on ebay. Difficult to clean and too cheap not to replace.

Most new frames come with cable guides through the frame that the workshop just throw away. Its like a really long thin straw that the inner slips through. You then remove the guide straw when the cable is installed. 

If you take a cost hit and buy your cables from your LBS this time,  ask them if they have any cable guide straws knocking about in the workshop which you can add to your 'tools' collection.

The way to stop the rattling inside the frame is to thread some of those donuts that are used to stop externally routed rear brake cables from touching the frame. Thread three or four donuts onto each of the sheaths / guides down which the gear cables will pass. Space the donuts out along the section of sheath that will be running the length of the inside of the down tube. The softer the donut material the better. Obviously this requires removing the sheaths from the frame first!

"Is one brand better than another for internal cables? I know they tend to supply different grommets and such."

Stick with major brands - Campagnolo, Jagwire, Shimano and Yokozuna. Inferior cables will use lesser grade stainless steel. Stay away from PTFE coated cables, you pay extra for the coating. The problem found with PTFE is the coating eventually wears away leaving you with a basic cable and ugly where it worn away.

"any tips to getting the cable through the frame?"

I've tried taping string to cable ends using electrical tape but found tape wrap was to thick to enter/exit the frame hole. Not knowing your frame I would try this method first. Be sure to clean the cable ends so the tape has something to grab onto. Test b4 pulling through frame. I use Super Glue and/or similar Krazy Glue. Clean the old AND new cable ends with acetone then glue the ends of each cable an inch or two (2-5cm). This will prevent ends from fraying.  Finally, glue 6 inches  (15cm) of string to one end of the old cable, then glue the other end of the string to the new cable. Pull slowly.

"The original cable had a slight tendency to rattle on bumpy roads, if I can I'd like to try and reduce or resolve this."

Ensure the cables are taught. You could try tie wraps/zip ties around cables where they enter the frame. Then another tie 3-4 inches (7.6-10cm) closer to the bars. Internal plastic tubing doesn't work as they would slap around too. Some people say small ties uncut (tail on) inside the frame. The loose ends would spring out against the internal walls and hold the cable in place. The hassle of removing uncut ties when it comes time to replace cables would be a big pia. IMO, don't use ties internally only externally.

HTH

Internal cables = vacuum & thread.

An easy way to pull through new cables, liners (to stop rattles) - thread liner & cable, tie thread to cable.  Use vacuum to suck thread through & out the frame tube.

As for cables - I've found just using new cables, outers of any reputable brand gives an improvement but I was most pleased with a recent Jagwire cable set.  Might as well change all the cables & the bar tape at the same time...a nice job for an icy afternoon when you can't ride.