When we whip cream by hand in a stainless steel bowl, with a metal whisk, small grey specks, ~0.5-1mm in size, appear in the cream. The specks are squishy and can easily be smeared out. See attached photos:     Googling does not turn up much except similar question at: http://chowhound.chow.com/topics/508107  The specks appear in different stainless steel bowls ("Stainless steel" imprinted on all bowls - no aluminium or other metals involved as far as we can tell).  The same whisk used in a plastic bowl does not produce specks.  The cream is organic, 40% fat (Swedish "Arla EKO"). We cannot detect any strange taste.  It seems probable that the specks come from mechanical wear. But what is it? What could be the cause? Is there something we should know about Stainless steel bowls? 
We just experienced the same phenomenon, and we were able to confirm that the specks were NOT bubbles - if we were careful enough, we could isolate the flecks.  They came in different shapes - some were specks, but some were almost filaments.  We have a stainless steel bowl, but we suspect the whisk was aluminum. Since aluminum is Mohs hardness 2-2.9 and stainless steel is 5.5-6.3, it's quite likely that the aluminum whisk was leaving residue on the side of the bowl that was ending up in the whipped cream.  We are avoiding aluminum utensils anyway, so now we will purchase a stainless steel whisk and see if the flecks still occur.    Update, October 26, 2015...  We've upgraded the whisk to stainless steel, and it still occurs when whipping cream in the stainless steel bowl.  I think the way to avoid flecks is to not use metal with metal, but instead use the whisk in a bamboo/plastic bowl. 