Are you filtering your water before using it (Brita, etc.) and do you have the Keurig water filter in the water tank? If you use well water especially, you'll get a metallic taste when the water heats and condenses a bit, concentrating metals in the water. If you remove the metals the coffee will not taste metallic, and your machine will last longer.
We have well water at home but just sediment filtered and naturally soft, no treatment is necessary other than calcite. I don't use filters in either coffee maker so they both get the same water. The kcup at work is the same way and I don't use it there either for the same reason. Maybe the kcup doesn't keep the water in contact with the coffee long enough? I don't know what the cause is, but I don't drink it.
Keurig actually is a drip coffee maker, and takes roughly the same time per cut that a drip brewer takes.
If you use a reusable kcup, it's sometimes the particular cup model that causes issues, both with the metal screening and the plastic. Having tested maybe a dozen different kinds, price is not a good indicator of quality.
Fine for drinking is not the same as fine for coffee brewing though. Filtered and distilled waters are the only types where all your brew methods will differ in taste only with factors associated with the coffee and the brewer's skill. Every other sort of water will taste very different with different brews. My in-laws' tap water tastes fine unfiltered for drip brew but for French press it's very odd.