How to safely o'scope Dell laptop adapters

[13hm13]

In EEV Blog #279, (at 09:25) Dave noted that his Dell laptop adapter has roughly 1K-ohm between mains earth (ground) and DC negative. This sets up a potentially hazardous situation for many o'scopes.

Dell makes great laptops (IMO) but their adapters are notorious for failing or getting noisy. So I have two basic question:

(1) WRT to the discussion of o'scope safety, how do I SAFELY use my Tektronix 465 (classic 1976 analog 'scope) with a now-failing Dell laptop adapter (it's similar to the one Dave showed in the episode  -- i.e, it is three-prong with an mains Earth prong).

(2) The "failing" adapter can be heard over the audio signal in terms of audible noise -- I have no noise using another (good) adapter; and with the "failing" one, I can make the noise go away for a while by gently (physically) tapping. It's been like this for several mos., but the adapter does now seem to be getting any worse -- i.e., a gentle tap every few days and I'm good to go until the noise comes back (after 3-4 days ... then just hit it again .
TTBOMK, related to the noisy adapter, I have not noted any (non-audio) other glitches in this laptops performance (its an Inspirion 1764, Win 7 laptop from July 2010). I am concerned that if I can hear the (switching?) noise, it's probab. not good for myriad other components comprising this laptop. Damage that "accumulates" over time. And this is why I want to SAFELY o'scope the adapter.

Thx!!

[Psi]

Run the laptop (power adapter) from and isolating transformer while working on it with the scope.