I also noticed this smell, when dissolving many metals (e.g. praseodymium metal, erbium metal, but also chromium metal). This is due to an impurity, present in most metals. Many metals come from phosphate ores and the refined and purified metal usually still contains some phosphorus. This phosphorus usually is present as phosphide and is formed during the arc/oven reduction of the metal ore. The last traces of phosphorous (usually only in the order of 0.01% to 0.1% of the weight) are not easily removed. When the metal is dissolved in acid, then this also dissolves, giving PH3 gas. This gas has a very typical smell and is very toxic. In the small amounts, you encountered, it is not that bad, but still, it is better to be careful not to breathe too much. The metal solutions themselves are odorless.